Calcium sulfate and barium sulfate inhibitors are used in a number of industrial applications to prevent precipitation and scale formation. Included among these are cooling water treatment, boiler water treatment, desalination, reverse osmosis, flash evaporators, and oil field recovery operations.
The biodegradability of polyaspartic acids makes them particularly valuable from the point of view of environmental acceptability and waste disposal. After polyaspartic acid has been utilized, it biodegrades to environmentally acceptable endproducts.
Thermal condensation of aspartic acid to produce polyaspartic acid is taught by Etsuo Kokufuta, et al., "Temperature Effect on the Molecular Weight and the Optical Purity of Anhydropolyaspartic Acid Prepared by Thermal Polycondensation", Bulletin of the Chemical Society Of Japan, Vol. 51 (5), 1555-1556 (1978).
Koaru Harada et al, U.S. Pat. No. 4,696,981 teaches the use of microwaves to produce anhydropolyaspartic acid from microwave irradiation of monoamonium, diammonium, monoamide, diamide and monoamideammonium salts of malic acid, maleic acid, fumaric acid and mixtures of these. Production of polyaspartic acid by partial hydrolysis of the anhydropolyaspartic acid with aqueous sodium bicarbonate is taught.
Other methods for producing polyaspartic acid are known. A number of these are referenced in U.S. Pat. No. 4,534,881. That patent teaches the use of certain polyaspartic acids for calcium carbonate inhibition.
It is also known that certain polyaspartic acids inhibit calcium phosphate crystallization. See "Inhibition of Calcium Carbonate and Phosphate Crystallization by Peptides Enriched in Aspartic Acid and Phosphoserine," by Sikes et al, ACS Symposium Series 444 (1991), pages 50-71.